This invention particularly relates to the design of keyboards that are very thin but which provide sufficient key travel for touch-typing purposes. The keyboards are particularly suitable for use in or with compact portable apparatuses such as notebook computers and personal digital assistants. However, the characteristic features of the invention can be incorporated in thicker keyboards and the keyboards, whether thicker or thinner keyboards, can be used with non-portable apparatuses.
Compact portable apparatuses such as notebook computers and personal digital assistants have become and will continue to become smaller and lighter because of the advancement of computer technology. However, the keyboard has remained something of a problem while the electronic parts reduce in size and weight. To allow for comfortable typing, and touch-typing in particular, the width and depth of a keyboard cannot be made too small because too close a spacing between small sized keys prevents comfortable and efficient typing, and particularly touch-typing. A foldable keyboard is one way of providing a keyboard which is large enough to allow touch-typing while enabling the width of the keyboard to be reduced when it is folded, for example, for the purpose of storing the keyboard in a compact apparatus. However, the only way left to reduce the overall volume of a keyboard, whether of the folding type or not, is to reduce the thickness of the keyboard, and in particular, to reduce the thickness of the keys of the keyboard.
Touch-typists like the keys of a keyboard to have a good feel when they are pressed. They should move downwardly in a stable manner when pressed and offer resistance to the fingers while doing so. The difficulties in constructing a very thin key while maintaining good feel can be explained by reference to FIG. 1. This figure shows a cross section illustrating the structure of a typical prior art key used in a thin keyboard. The key 10 comprises a key cap 11 and a silicon rubber support 12 to which the key cap is mounted and which spaces the key cap above a printed circuit board 13. When a finger presses the key at point A, the resilient flexibility of the rubber support 12 allows its deformation whereby the key cap 11 is lowered vertically and evenly to enable a projection 14 of the support 12 to make contact with the printed circuit board 13. The projection 14 functions as a switch means enabling the pressing of the key to be registered when it contacts the printed circuit board. However, if the key 10 is pressed off-center at point B, the key cap 11 may tilt. In this case, there will not be a good feel about the movement of the key and, furthermore, a proper contact between the projection 14 and the printed circuit board 13 might not be made.
Lever mechanisms are often used to make sure that the whole key cap can travel evenly and vertically when pressed. Such mechanisms are normally placed beneath the key cap and above a support plate, such as a printed circuit board. Each key has its own individual lever mechanism supporting it. In a typical key structure such as that shown in FIG. 1, it can be seen that the keyboard cannot be made very thin because there is firstly a need to have a silicon rubber support 12 or other spring-like mechanism beneath the key cap 11 and there is secondly a need to have a lever mechanism placed beneath the key cap for stabilization purposes. For the key to have reasonably good feel for touch-typing, the key travel needs to be at least 2-4 mm. Even with a key travel of 2 mm, the thinnest keyboard constructed with the type of key shown in FIG. 1 is not likely to have a thickness of less than about 5.5 mm.
U.S. Pat. No. 5,424,516 (Emmons) and U.S. Pat. No. 5,519,569 (Sellers) show ways of constructing lever mechanisms to reduce the overall thickness of the keys, and hence of the keyboard. However, the presence of the lever mechanisms placed beneath the key caps still places a limit on the degree to which the thickness of the keys, and hence the keyboards, can be reduced.
In other keyboards, lever mechanisms are not used and other approaches are taken to try and obtain uniform vertical movement of the keys when pressed. Examples are given in European Patent Publications 88,365 and 556,426 and in U.S. Pat. No. 5,422,477 (Spence).
As to the overall width of the keyboard, U.S. Pat. No. 3,940,758 (Margolin) shows a folding keyboard. However, as already indicated, while a folding keyboard allows the width of a keyboard to be reduce for storage, the thickness of the folded keyboard is increased. In other words, the volume occupied by the keyboard is not reduced.
There is therefore a need to provide a keyboard having a small volume, that is, a thin keyboard, which keyboard has key caps which travel evenly and substantially vertically when pressed and which, preferably allow for a good touch-typing feel.
An object of the invention is to provide a thin keyboard having keys with key caps having a good degree of travel and stability. A preferred object is that these features, together with the spacing of the keys, is such as to allow for touch-typing. Another object of the invention is to provide a thin keyboard, which is particularly suitable for use with portable apparatuses, and which can be manufactured at relatively low cost. However, as has already been indicated, the essential characteristics of the present invention can be incorporated in thicker keyboards if that should be desired.
The present invention broadly consists of a keyboard including a substantially rigid base plate; supporting means for supporting the base plate so as to be movable between an extended position and a retracted position; biasing means biasing the base plate to the extended position; a plurality of keys arrayed over an outer surface of the base plate; and a switch means associated with each key; wherein, when any key is pressed sufficiently firmly, the supported base plate moves against the action of the biasing means substantially from the extended position to the retracted position thereby providing for at least some travel of the pressed key, and the switch means associated with the pressed key enables the registration of the pressed key, and wherein release of the pressed key allows the base plate to return to the extended position under the action of the biasing means.
From this, it will be realised that according to the present invention, the travel of the pressed key is provided, at least in part, by the movement of the base plate.
In a preferred embodiment of the invention, each key includes a key cap biased to a raised position spaced from the base plate and movable to a depressed position against the base plate when an outer face of the key cap is pressed sufficiently firmly. The pressing of any key sufficiently firmly to move the base plate from its extended position to its retracted position is also sufficient to move the key cap of that key from its raised position to its depressed position. In this embodiment, the full travel of the key cap is provided by two movements. There is firstly the small degree of movement of the key cap from its raised position to its depressed position against the base plate and then there is the movement of the base plate from its extended position to its retracted position. It is the movement of the base plate which preferably provides most of the overall movement of the key cap. The main purpose of the initial movement of the key cap from its raised position to its depressed position is to actuate the switch means associated with the pressed key enabling its registration.
The switch means associated with each key preferably includes an electrical circuit closing means on an inner face of the key cap and separated electrical contacts on the base plate corresponding to that key. The electrical circuit closing means makes contact with and closes the corresponding electrical contacts on the base plate when the key cap is pressed to its depressed position. The base plate preferably includes a printed circuit board.
In the preferred embodiment of the invention, the outer surface of the base plate is covered by a sheet of material having the plurality of keys on the sheet, and preferably integrally formed in the sheet. The preferred sheet is a sheet of resilient material and the resilience of the material biases each key cap to its raised position while allowing the key cap to be moved to its depressed position.
In one embodiment of the invention, the sheet is not attached to the base plate and in such an embodiment, the supporting means preferably includes a frame extending substantially about the base plate with the sheet being attached to that frame. However, in another embodiment, the sheet is attached to the base plate.
In one embodiment, the supporting means includes a plurality of feet attached to the base plate at a side opposite that surface having the plurality of keys. Placement of the feet on a supporting surface supports the base plate clear of the supporting surface. The biasing means includes the feet being resiliently compressible, for example, by being made from a resiliently compressible material, so that when a key is pressed sufficiently firmly the feet compress and the base plate thereby moves from its extended position to its retracted position. The feet may be formed simply of a piece of resilient material or, alternatively, the feet may be formed of a suitably shaped, resilient material which when depressed will create a definite click feel. The supporting means may also includes a frame with which the plurality of feet engage. However, it is not necessary for there to be a frame. Where there is no frame, the feet may be placed directly on a supporting surface such as a desk top. In this case, the keyboard would normally be separate from the apparatus with which it is being used, except for electrical or other connections between the keyboard and the apparatus. Such an apparatus may be a notebook computer or a personal digital assistant, for example. Where the supporting means includes a frame, the keyboard may either be separate from, or incorporated in as part of, the apparatus with which the keyboard is being used.
In another embodiment where the supporting means includes a frame, the supporting means also includes an arm attached to each of top and bottom edges of the base plate. The arms extend in parallel beyond a side edge of the base plate and are pivotally attached at their distal ends to the frame. This allows the base plate to undergo some pivotal movement relative to the frame between the extended and retracted positions of the base plate. In this embodiment the biasing means may includes at least one spring-loaded microswitch between the frame and the base plate at an opposite end of the base plate. The use of a microswitch is to provide a positive click when a key is pressed to improve the tactile response of the key for the user of the keyboard. Spring-loaded microswitches may be used as the biasing means in other embodiments of the inventions as well. Alternatively, a suitably shaped resiliently compressible material can also provide a click feeling, as described above.
The keyboard can have two, or even more, base plates arranged side-by-side. Each base plate is movable between its extended position and its retracted position independently of the other. The multiple base plates may be interconnected by one or more flexible printed circuit boards or other types of electrical or other connections.
In one embodiment where there are at least two base plates, these base plates are pivotally connected relative to each other so that one base plate can be folded against the other. In this way the width of the keyboard can be reduced for storage or carrying of the keyboard.
In another embodiment of the invention, the supporting means includes a pair of interconnected lever arms pivotally connected to the base plate at an edge of the base plate and another pair of interconnected lever arms pivotally connected to the base plate at an opposite edge of the base plate. At least one arm of one pair of arms is connected to an arm of the other pair of arms so that the lever arms pivot together and as they do the base plate moves uniformly between its extended and retracted positions. The lever arms of each pair of lever arms are preferably interconnected by an axle portion and it is the axle portion which is pivotally connected to the respective edge of the base plate. All of the lever arms preferably lie clear of the base plate for all pivotal positions of the arms between the extended and retracted positions of the base plate, and in the retracted position of the base plate the arms lie in the plane of the base plate. The purpose of this is to achieve as thin a keyboard as possible. In this embodiment, the supporting means may also include a frame with which the distal ends of the arms are pivotally engaged. The biasing means is preferably a spring which acts on at least one of the lever arms to bias all of them to positions where the base plate is in its extended position.